The medial terminal nucleus or the nucleus of the basal optic root (nBOR) of the accessory optic system receives an exclusive input from the displaced retinal ganglion cells of Dogiel. The displaced ganglion cells (DGC) are distributed predominantly within peripheral portions of retina and are characterized by their location at the border of the inner plexiform layer (IPL) and the inner nuclear layer, their large size (20m x 30m), and dendrites which ramify only within the 1st strata of the IPL. We plan on continuing study of the DGC at both the light and electron microscopic levels. The electron microscopic studies are designed to characterize the DGC and the synaptic contacts found upon it. The light microscopic studies will attempt to identify the transmitter of the DGC using high affinity uptake studies of putative neurotransmitters. The nBOR gives rise to direct projections upon the oculomotor nuclear complex, trochlear nucleus, vestibulocerebellum and the medial division of the inferior olivery complex. We plan quantitative studies of the nBOR including cell size, type and appearance. Electronmicroscopic studies will include characterization of DGC terminals and their relationship to nBOR neurons. Studies of the nBOR projection patterns and synaptic terminal patterns within the oculomotor complex and vestibulocerebellum are planned. We also plan to characterize the developmental sequence of the nBOR and compare this to the developmental sequences of other central visual nuclei.